In an MRI system the image of a sample or specimen is determined by a static or dc magnetic field and several gradient fields. For example, typical gradient fields will consist of three nominally orthogonal gradient fields known as phase encoding, slice select and readout. Where the static magnetic field is inhomogeneous and the gradient fields nonlinear this results in a geometrically distorted or warped image. Such image is reconstructed from the signals generated by the various gradients typically by a Fourier transform reconstructive technique.
It is known that the above distortions can be corrected by mapping the static magnetic field and the gradient fields. Then a restoration algorithm is applied to correct the distortion and this provide a corrected image. One restoration technique is described in an article in Medical Physics, 12(1) Jan./Feb. 1985, entitled "NMR Imaging in the Presence of Magnetic Field Inhomogeneities and Gradient Field Non-Linearities" by O'Donnell and Edelstein. Another similar article is entitled "NMR Imaging For Magnets With Large Non-Uniformities" by Sekihara. et al., IEEE Transactions On Medical Imaging, Dec. 1985, Vol. 4, No. 4, pp. 193-199. However, the straightforward application of the reconstruction technique such as that shown in the above Medical Physics article may result in an unacceptable image. Specifically, the corrected image may have noise artifacts.